Oligosaccharide modeling

For the synthesis of HA oligosaccharides, model glycosylations were carried out in solution and on PEG support. A glucosamine acceptor coupled with hydrojyl-terminated PEG monomethyl ether 11 was efficiently glycosylated with trichloroacetimidate donor 10 afford an orthogonally protected disaccharide 12 which can be used for the synthesis of HA sequences, see Scheme 3. 

Hydrolysis Rate Constants for Model Oligosaccharides with Lysozyme... 

Hen egg-white lysozyme catalyzes the hydrolysis of various oligosaccharides, especially those of bacterial cell walls. The elucidation of the X-ray structure of this enzyme by David Phillips and co-workers (Ref. 1) provided the first glimpse of the structure of an enzyme-active site. The determination of the structure of this enzyme with trisaccharide competitive inhibitors and biochemical studies led to a detailed model for lysozyme and its hexa N-acetyl glucoseamine (hexa-NAG) substrate (Fig. 6.1). These studies identified the C-O bond between the D and E residues of the substrate as the bond which is being specifically cleaved by the enzyme and located the residues Glu 37 and Asp 52 as the major catalytic residues. The initial structural studies led to various proposals of how catalysis might take place. Here we consider these proposals and show how to examine their validity by computer modeling approaches. 

LD model, see Langevin dipoles model (LD) Linear free-energy relationships, see Free energy relationships, linear Linear response approximation, 92,215 London, see Heitler-London model Lysine, structure of, 110 Lysozyme, (hen egg white), 153-169,154. See also Oligosaccharide hydrolysis active site of, 157-159, 167-169, 181 calibration of EVB surfaces, 162,162-166, 166... 

Subtilisin, 170 active site of, 171,173 autocorrelation function of, 216, 216 potential surfaces for, 218 site-specific mutations, 184, 185, 187-188 Sugars, see Oligosaccharides Surface-constrained solvent model, 125... 

Another reason is that xylo-oligosaccharides of defined structure are very important substrates that serve as model compounds for the optimization of hydrolytic processes and in enzymic assays. The enormous development... 

Figure 41-7. The fluid mosaic model of membrane structure. The membrane consists of a bimolecu-lar lipid layer with proteins inserted in it or bound to either surface. Integral membrane proteins are firmly embedded in the lipid layers. Some of these proteins completely span the bilayer and are called transmembrane proteins, while others are embedded in either the outer or inner leaflet of the lipid bilayer. Loosely bound to the outer or inner surface of the membrane are the peripheral proteins. Many of the proteins and lipids have externally exposed oligosaccharide chains. (Reproduced, with permission, from Junqueira LC, Carneiro J Basic Histology. Text Atlas, 10th ed. McGraw-Hill, 2003.)...

BUDDINGTON R K, KELLY-QUAGLIANA K, BUDDINGTON K K, KIMURA Y (2002b) Non-digeStible oligosaccharides and defense functions lessons learned from animal models. Br J Nutr. 87 S231-9. 

D-Gal — hydroxy-L-histidine,4950 d-G1cA — hydroxy-L-tryptophan,51 d-GlcA — hydroxy-L-phenylalanine,51 d-G1cA — L-Ser,51 and carbohydrates N-glycosylated to the a-amino group of the N-terminal portion of proteins.51-53 Most of these compounds will be discussed in more depth later in this article, in terms of model compounds for oligosaccharide linkages to proteins. 

Early conformational studies by HOESY experiments are illustrated by the work of Batta and Kover54 who were able to access oligosaccharide sequencing and conformational distribution around the glycosidic bond in model compounds. These determinations make use of relayed proton-proton-carbon cross-relaxation. 

The novel L-lysine modified cross-linked chitosan resin containing imine linkers [15] has been studied by the 13C CP MAS spectroscopy.31 However, as some ambiguous results were obtained and the resin was insoluble, instead of the resin a soluble model compound, derivative of chitosan oligosaccharide, has been obtained and investigated. 

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